In many cases, production of semiconductor modules (also referred to herein as “modules” or “integrated circuit (IC) modules”) is performed in several processes. These processes may be performed by distinct entities at distinct locations. Initially, wafers are formed (e.g., silicon wafers) from bulk silicon; those wafers are then diced into chips (frequently in a group of substantially identical chips); those chips are then fitted with their appropriate connecting components and external circuitry to form a semiconductor device; and finally, those devices are packaged to form one or more modules which can be utilized for a particular purpose such as data storage, transmission, logic, transmission, etc.
In performing each of the above-noted processes of making a module, a percentage of the wafers, chips, devices and/or modules can be discarded due to a failure to meet particular specifications of a subsequent process. The percentage of the wafers, chips, devices, and ultimately modules that remains after production is considered the overall yield (percentage) of the process. Within that overall yield is a percentage yield in forming the wafers from the bulk silicon (wafer yield), a percentage yield in forming the chips from the wafers (chip yield), a percentage yield in forming the devices from the chips (device yield), and a percentage yield in forming the modules from the devices (module yield).
Prior methodologies involved a customer approaching a manufacturer (e.g., a foundry) to produce X number of modules based upon a particular design Y. The manufacturer would then take the bulk silicon, form wafers, chips, devices, and eventually, modules based upon the customer order. After each process, a percentage of the product is passed to the next process (yield), and a percentage is discarded because it does not meet specifications.
In some cases, customers have provided their own design for the module, and asked the manufacturer to produce the module based upon their design. Various manufacturers would produce the module and absorb the cost of the yield(s), which in some cases were attributable to the customer's design. However, absorbing the cost of the yield(s) can negatively affect the profitability of the manufacturing process
A more recent approach has been to use a multi-part order without yield liability. In this case, the customer may approach the manufacturer to request Z number of wafers (from a bulk silicon), but the customer remains liable (financially responsible) for the yield. The manufacturer can test the wafers to determine yield, and the customer pays for any discarded product. In this model, the customer often then asks the manufacturer to produce chips, devices and modules from the wafer, but takes responsibility for at least one portion of the overall yield (e.g., the wafer yield).
While this recent approach has helped manufactures to reduce financial liability for yield, prior modeling approaches for predicting and accounting for yield in these processes are insufficient to address this scenario.